Ordinarily, SMS messages are communicated from a message sender to a message recipient in the following manner, defined by Global System for Mobile Communications (GSM) technical specification 03.40. First, the sender creates a message to be delivered (e.g., by typing it into the keypad of a mobile telephone), and specifies the recipient for the message (e.g., by typing a mobile phone number for the intended recipient of the message). The message would then be sent from the sender to his or her SMS service center (SMSC) which would query a database called a home location register (HLR) to identify how to route the message, and would then send the message to the intended recipient based on the information received from the HLR. If the recipient receives the message (e.g., it was sent to a mobile phone which was on and had an active subscription), the SMSC would receive a delivery confirmation message. If the recipient does not receive the message (e.g., if it was sent to a mobile number which was turned off), then the SMSC would retry sending the message until it either receives a delivery confirmation, or a predefined message storage period (e.g., two weeks) expires.
While the above approach has proved effective in delivering messages in cases where a recipient can be located accurately using information in the HLR, it is not always sufficient in more complex scenarios. For example, if an intended recipient has multiple numbers, an SMS message addressed to one of the recipient's inactive numbers might not reach the recipient (or might only reach the recipient if the recipient reactivates the inactive number), even though the recipient might have an active subscription when the SMS message was sent. Similarly, in cases where the number for an intended recipient is mutable (e.g., where a subscriber can switch between active numbers), the standard delivery and retry mechanisms could fail, with the SMSC trying to redeliver the message to the original (inactive) number, rather than being able to adapt to the changes made by the subscriber. As a result, there is a need in the art for technology which can allow SMS messages to be delivered properly even in cases where a recipient has multiple (potentially changeable) numbers.